I. Field
The present disclosure relates to wireless transmission in general and in particular to wireless transmissions using multiple spatial streams and pilot tones.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communication systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing channel resources while achieving high data throughputs. Multiple-Input and Multiple-Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards, such as the Institute of Electrical Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
Spatial Division Multiple Access (SDMA) is a multiple access scheme that enables multiple streams transmitted to different receivers at the same time to share the same frequency channel and, as a result, provide higher user capacity. SDMA is a common and typical MIMO scheme in cellular wireless systems.
Traditionally, pilot tones are used to assist with transmission and reception. In SDMA systems, pilot tones might be transmitted using multiple transmit spatial streams by cycling through spatial streams. However, spectral flatness becomes an issue and pilot tracking for a particular pilot tone may fail if fading occurs on the spatial stream that happens to be carrying the pilot tone.